What Biblical justifications are used for having separate denominations?

I think the key here is the word church. A church can mean a building (often it's a kind of temple with an later), or it can mean an group whose membership implies commitment to a particular creed and may involve an earthly authority over its members. The word church in the bible just means a group of believers who met together.

When the bible was first translated into English, the word "church" didn't occur in it: the word used was "congregation". The people who read it and understood it, wanted nothing to do with the Church.

In part, further divisions came about when new churches were formed and people wanted to separate themselves from what they saw as false teachings. The biblical justification, and cause of division, I think is evident in:

17 Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them. 18 For they that are such serve not our Lord Jesus Christ, but their own belly; and by good words and fair speeches deceive the hearts of the simple. Romans 16:17-18

There is a difference between the unity of the Church, bringing people under a single earthly authority and doctrines that men teach for money, and the unity of Christians under Christ in the doctrine which is described in scripture and the Holy Spirit teaches.

There is plenty of relevant scripture especially in the later books of the New Testament. See for example 2 Peter.

If you continue reading until 1 Corinthians 3, you will see that division is a sign of immaturity. And as baby Christians, we need to grow, desiring the milk of the word. See 1 Peter 2:2

Definitely unity among Christians is a good thing.

But sometimes we just cannot not to separate, as justified by the following New Testament verse:

(2Cor. 6:17)

Therefore “‘Come out from among them, and be separate,’ says the Lord. ‘Touch no unclean thing. I will receive you. I will be to you a Father. You will be to me sons and daughters,’ says the Lord Almighty.”

We need to be separated when there is not other way.

They say that Luther separated from Catholic church. But I would say that the Catholic church separated from Lutherans: It is a pope who anathematized Luther.

They say that Pentecostals separated from Baptists. But I would say that Baptists separated Pentecostals by their anti-Pentecostal declaration. If Baptists didn't separate Pentecostals, they would probably continued with each other in peace.

So as I see: We should not separate, but we can be separated by others.

I don't know that you could term it a "justification", but a Biblical basis for understanding why so many different denominations exist can be found in the same letter to the Corinthians that you cite (11:19):

For there must be also heresies among you, that they which are approved may be made manifest among you.

The NASB (from which I think you are quoting) softens this a bit to:

For there must also be factions among you, so that those who are approved may become evident among you.

But the word chosen in the King James seems to be much closer to the Greek αἵρεσις - hairesis.

There is a reluctance today - perhaps understandable - among Christians to label those of other denominations as "heretics". But difference in doctrine is what principally "denominates" denominations. It is logically impossible for all existing denominations to hold true teachings, when all generally conflict with one other. Either all existing denominations are teaching at least some false doctrine, or exactly one is not.

Rather than answer all the questions I'm going to stick with the main question.

Q. What is the Biblical justification for different denominations?

A. What is the Biblical justification for one Church?

There should never have been different denominations (or branches of belief) but as Paul stated here in Eph 4:1-16. There is only one body of believers, the Church.

...

3 Endeavouring to keep the unity of the Spirit in the bond of peace.

4 There is one body, and one Spirit, even as ye are called in one hope of your calling;

5 One Lord, one faith, one baptism,

...

14 That we henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men, and cunning craftiness, whereby they lie in wait to deceive;

15 But speaking the truth in love, may grow up into him in all things, which is the head, even Christ:

16 From whom the whole body fitly joined together and compacted by that which every joint supplieth, according to the effectual working in the measure of every part, maketh increase of the body unto the edifying of itself in love.

Paul did grapple with the beginnings of denominations in his day too. It was because the believers brought in traditions and beliefs from the old testament law that they thought were still required, such as circumcision.

Why did it occur? because of many reasons. But you could say simply that it's because the people who have started these denominations haven't believed and followed the one who is to guide us into all truth. So instead they have substituted it with corrupted understanding and taught this corruption to others who do not have the knowledge.

Another reason can be because of poor translating. There are many words added in some translations that are not there in the original text. These words are added to help clarify the text but sometimes they change the meaning. At least the King James writers had the integrity to italicise added words.

Even with poor translation though, the Holy Spirit can still guide you into truth. And the only way to be guided is to walk in the spirit as in Romans 8. We need to study the text and ask the right questions. Did you not know that you can ask the Holy Spirit in you questions about what you're reading? In the end it comes down to a relationship with Jesus. Not everyone in the church has a relationship. This is why Jesus said in Matt 7:21-23 -

21 Not every one that says unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that does the will of my Father who is in heaven.

22 Many will say to me in that day, Lord, Lord, have we not prophesied in your name? and in your name have cast out demons? and in your name done many wonderful works?

23 And then will I profess unto them, I never knew you: depart from me, you that work iniquity.

It's because it's all about the relationship.